In general, three-platen type mold-clamping apparatuses having stationary, movable and rear platens, have been employed in molding machines such as injection molding machines. The mold-clamping apparatus of this kind are designed to use a toggle mechanism, a crank mechanism or a ball-screw/ball-nut mechanism to reciprocate the movable platen along a plurality of parallel tie bars which extend between and interconnect the stationary platen and the rear platen for mold-opening, mold-closing and mold-clamping operations. Such mold-clamping apparatus is arranged so that the tie bars may be elongated, during the mold-clamping operation, for generating a mold clamping force. And respective ends of the tie bars are supported by the rear platen to establish and maintain a constant parallel relationship between the stationary and movable platens. These conventional three-platen type mold-clamping apparatuses inevitably include a plurality of tie bars and the rear plate. However, these components are expensive, and it is therefore difficult to produce a three platen mold-clamping apparatus which is low-priced and free from complicated maintenance.